Jim Gathany / Centers for Disesase Control via EPA

A Culex quinquefaciatus female mosquito feeds on human blood. This species is a known vector for West Nile Virus.

DALLAS —When Dr. Robert Haley spotted a dead blue jay lying in his neighbor's driveway early this summer he became suspicious. When he saw another blue jay dead in the birdbath at his Dallas home the next morning, he knew it was a bad omen of disease.

What he could not predict at the time was that the bird corpses heralded one of the worst U.S. outbreaks of West Nile virus on record, with nearly 40 percent of cases in Texas alone.

"It's unusual to see dead birds lying in the open," said Haley, chief of epidemiology at the University of Texas Southwestern Medical Center. "Typically, birds die in some out-of-sight place or they are carried off by animals if they die out in the open."

West Nile is transmitted from sick birds to humans and other mammals by mosquitoes and was first detected in the United States 13 years ago, in New York City. Texas declared a state of emergency last month after seeing the worst toll from West Nile this year, which has reached 3,545 total cases and 147 deaths nationwide, according to the U.S. Centers for Disease Control and Prevention. Other states with large outbreaks include Mississippi, Michigan, South Dakota, Louisiana, Oklahoma and California.

"From the beginning, I thought it could be a bad year," said Haley, who spent 10 years working for the CDC and now lives in the epicenter of the outbreak. "But it turned out to be much worse than anyone imagined. It was a public health disaster."

More than 400 new U.S. cases of West Nile virus emerged in the last week, in an outbreak that remains one of the worst of record but has begun to show signs of slowing down. Experts hope the outbreak has peaked as cooler weather sets in and widespread pesticide spraying takes effect. Now is the time to learn the lessons for the future.

Good weather for mosquitoes
Five counties within the Dallas-Fort Worth area — the fourth largest metropolitan area in the country — recorded 28 of the 63 deaths and 869 of the 1,429 cases reported to the Texas Department of State Health Services by Tuesday. Dallas County alone has recorded 16 deaths and 371 cases, according to county authorities.

CDC and state officials believe a year's worth of record high temperatures and intermittent rainfall this past spring contributed to the severity of the epidemic by affecting bird and mosquito populations. Following a record hot summer and drought conditions in 2011, Dallas-Fort Worth had a warm winter with fewer than normal freezes followed by bouts of rain in the spring, officials said.

"One of the things we are closely looking at is the effect of weather on this year's outbreak," said Lyle Petersen, director of the CDC's Division of Vector-Borne Infectious Diseases. "West Nile outbreaks tend to be difficult to predict. Why it occurred in Dallas more than other areas is a matter of speculation at this point, and it's something that we're going to be looking at very carefully."

In addition, health officials in the region have witnessed an especially large number of neuroinvasive cases, the more severe form of the disease that often leads to meningitis and encephalitis.

Haley estimates that about 25,000 people likely were infected with West Nile in Dallas County this summer. Of those, about 80 percent showed no symptoms at all, while many of the remaining residents came down with West Nile Fever, a mild form of the disease that is largely under-reported and only sporadically tested. State figures show only that Dallas County recorded 168 West Nile fever cases and 154 neuroinvasive cases.

Death toll may rise
Haley and others say the worst should be over in terms of new infections, but more cases are expected to be reported due to the lag time between infection, testing for the virus and reporting to state agencies and the CDC. The death toll is also likely to rise as it can take weeks to months for patients to deteriorate.

In the meantime, Dallas residents are still coming to terms with the ravages of the outbreak, which dwarfs the four deaths seen in the region in 2006.

With no vaccine to prevent West Nile in humans, the only defense is prevention — wearing insecticide outdoors and pesticide spraying by ground and air.

Dr. Don Read, a surgeon in Dallas who was infected by neuroinvasive West Nile in 2005 while walking in his Dallas neighborhood and now runs a support group for survivors, said people tend to think they are invincible. "I didn't think I would get it until I did. It only takes one mosquito bite."

Read, who was infected at age 63, spent almost five weeks in the intensive care unit. He now wears braces on his legs due to polio-like paralysis, but considers himself lucky to be alive.

The sound of a plane buzzing overhead spreading insecticide in the suburban community of Southlake was a welcome sound to Ann Dachniwsky, 47, who spent much of the summer so fatigued from neuroinvasive West Nile that her only activity was "going from the bed to the couch back to the bed."

At the height of her illness, her husband and three children took turns waking her up every few hours to force her to drink.

"My balance and sight were affected so I could barely work or see. I was flat on my back for weeks," she said. "I was a healthy, active person. I'm getting better but I can barely manage one activity without needing to lay down afterwards."

Dachniwsky's family had pleaded with the Southlake City Council to allow aerial spraying of pesticide for the first time since an encephalitis outbreak nearly 50 years ago. Dallas and nearby Denton counties conducted aerial spraying missions in August. Southlake, which is partially in Denton and Tarrant counties, was sprayed. Officials in Tarrant County, home of Fort Worth, chose to spray only by ground.

As the outbreak has slowed, Dallas County health officials continue to be criticized both for not moving fast enough to start spraying and also for going too far in the breadth of the aerial spraying program once it started.

"We had a protocol in place and we followed it," said Zach Thompson, director of the Dallas County Department of Health and Human Services. "We started with public education, followed by localized ground spraying, then enhanced ground spraying and finally aerial spraying."

As research and analysis of the outbreak continue, Thompson said officials will work diligently to avoid a repeat of history.

"We were surprised by the magnitude of the outbreak this year but we feel that our response was appropriate," Thompson said. "Hindsight is 20/20." 

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